1. Field of the Invention
The present invention relates to a fuel injection device used for an internal combustion engine, a driving method and a driver circuit for the fuel injection.
2. Background Art
In recent years, from the viewpoints of the tougher control of carbon dioxide emission and concerns about exhaustion of fossil fuels, lower fuel consumption for an internal combustion engine has been demanded. For that reason, an effort to decrease the fuel consumption has been exerted by a reduction of various losses in the internal combustion engine. In general, when the losses are reduced, an output necessary for driving the engine is lowered with the result that the lowest output of the internal combustion engine is also lowered.
In the above internal combustion engine, there is a need to control the amount of fuel to be small enough for the lowest output for feeding the fuel. In recent years, as a technique for decreasing the fuel consumption of the internal combustion engine, there is a downsized engine that is downsized with a reduction in the displacement, and the output is obtained by a supercharger. In the downsized engine, because a reduction in the displacement enables a pumping loss and a friction to be reduced, the fuel consumption can be decreased. On the other hand, the supercharger is used to obtain a sufficient output, and a reduction in compression ratio associated with supercharging is suppressed by suction cooling effect of direct injection to realize the low fuel consumption. In particular, in the fuel injection device used for the downsized engine, there is a need to inject fuel over a wide range from the smallest amount of injection corresponding to the lowest output obtained by reducing the displacement to the largest amount of injection corresponding to the highest output obtained by supercharging. Accordingly, in order to decrease the fuel consumption, there is a need to reduce the smallest amount of injection that can be controlled by the fuel injection device. For the purpose of injecting a small amount of fuel, there is a method of controlling the amount of lift of the valve to a position lower than a full open position. For example, Japanese Patent Unexamined Application Publication No. 2000-27725 discloses a method for a fuel injection device in which the amount of leakage of a high-pressure fuel from a pressure control chamber is determined according to the amount of lift of an on-off valve disposed upstream of a needle valve, and the lift of the needle valve, that is, a fuel injection rate is controlled according to a pressure drop in the pressure control chamber to inject the small amount of fuel.
Also, Japanese Patent Unexamined Application Publication No. 2002-70682 discloses a method for a fuel injection device in which a pressure within the pressure control chamber is controlled by a pressure control value, the pressure control chamber is tightly sealed with the pressure control chamber, and the needle valve is stopped at an arbitrary lift position between a full open position and a full close position by the tightly sealed pressure control chamber.